MINGORA (Reuters) -- Pakistani security forces killed at least 15 Taliban militants, including a commander, in clashes today in the volatile northwest near the Afghan border.

Nuclear-armed Pakistan is under growing U.S pressure to crack down harder on militants in border areas to help it fight the Taliban in Afghanistan, where President Barack Obama plans to send 30,000 more troops to try to put down an insurgency.

Obama said in a speech on December 1 the United States would not tolerate Pakistan allowing its territory to be a safe haven for militants and urged it to fight the "cancer" of extremism.

The latest clashes took place in the northwestern Swat valley, two days after a teenage suicide bomber killed an anti-Taliban lawmaker in the region.

The army, battling a Taliban insurgency, launched what it said was a successful offensive in Swat in late April that cleared most of the area, but it still faces pockets of resistance.

A Taliban commander Nasim Shah, alias Abu Faraj, was killed in the fighting that erupted after security forces raided a militant hideout in the Kabal area of the valley.

"One soldier was wounded while 11 militants including Abu Faraj was killed," military spokesman Major Mushtaq Ahmed said.

Abu Faraj was a close associate of Fazlullah, the Taliban leader in Swat who told the BBC last month he fled to Afghanistan and would launch attacks against the Pakistani army from there.

Four militants were killed in clashes elsewhere in the valley, a security official said.

Separately, security forces arrested 13 militants, including three commanders, in Khyber, a tribal region where convoys carrying supplies for Western forces in Afghanistan are frequently attacked, said a statement from the Frontier Corps paramilitary force.

In his address, Obama said the United States would help Pakistan root out militants in the tribal border area.

Pakistan is worried that the U.S. troop surge could send Taliban militants fleeing to its territory, particularly in the southwestern Baluchistan province where it is struggling to end a low-level insurgency.

Pakistani security forces killed more than 2,000 fighters in Swat, about 120 kilometers northwest of Islamabad, in the offensive, according to the army. There has been no independent verification of that casualty estimate.

The army launched a major offensive against the militants in their South Waziristan bastion on the Afghan border in mid-October. The militants responded with a spate of bombings, killing hundreds of people.

Four people, including two policemen, were wounded in a roadside bomb blast in the city of Peshawar on December 3